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blumenkraft

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Re: PIG has calved
« Reply #1150 on: November 19, 2019, 07:18:47 PM »
Post 1337! I devote leet post to a bold (and perhaps silly) question.

When Baking said that the 'shelf itself is generally pretty stable' these days that made me think what if it isn't?

Perhaps these cracks are a sign that the floating part of the glacier is separating from the grounded part?
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paolo

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Re: PIG has calved
« Reply #1151 on: November 19, 2019, 07:43:55 PM »
Stephan,
I agree with Baking that it is the long term that is important and that the short term is only anecdotal.

In addition, given:

1.   that the information we have: Sentinel, relates only to the surface and not to the 3D structure

2.   and that the small-scale framework of existing tensions (what would be needed for accurate short-term forecasts) is largely unknown and rather chaotic

it seems clear to me that we do not have the means to make short-term forecasts.

That said, it's fun to make predictions:
1.   THE PIG/SWT seal could break in early December
2.   The rift2 (the more internal one) should join the rift of the joint PIG/SWT (previous point) either when the joint break or little time after (say before Christmas)
3.   The rift1 will have joined the rift2 before Christmas
4.   Extending at least one of two rifts to the NSM will take longer, say late January or early February
5.   The iceberg detachment could be for February.

But I wouldn't play money on it

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Re: PIG has calved
« Reply #1152 on: November 19, 2019, 08:30:01 PM »
blumenkraft,
as can be seen at the bottom of the screen the latitude and longitude of the two images are not the same!
Plus grounded doesn't mean still
In a margin shear there can be either plastic deformation or the creation of rifts that they can weld later


blumenkraft

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Re: PIG has calved
« Reply #1153 on: November 19, 2019, 08:37:01 PM »
Thanks for your answer, Paolo.

The latitude and longitude shown indicates where the cursor is on the screen. The pictures are correctly aligned.

Your second point is very interesting though. Would you say the deeper the rift, the greater the deformation on top?
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blumenkraft

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Re: PIG has calved
« Reply #1154 on: November 19, 2019, 08:49:36 PM »
And this is an iceberg inside the (big downstream) crack that flipped to the side, showing exactly how thick (or better to say thin) the ice is.

That's so cool. You can clearly see them as those darker spots in the SAR imagery.

Link >> http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201911/S1B_IW_GRDH_1SSH_20191119T092639_8DD8_S_1.8bit.jp2
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Tor Bejnar

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Re: PIG has calved
« Reply #1155 on: November 19, 2019, 09:31:30 PM »
So ... how many pixels thick (thin) yields how many arbitrary units of measurement (meters?)?
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paolo

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Re: PIG has calved
« Reply #1156 on: November 19, 2019, 10:32:37 PM »
blumenkraft,

To create the animated gif you have aligned the two images on an iceberg, origin PIG (that's why the PIG itself has a residual movement, i.e. the iceberg is slightly slowed down relative to the PIG).

As for the SIS it is normal that it does not move like the PIG, it is for this reason:
1.   that he has a shear margin between PIG and SIS
2.   that by aligning the images on the PIG the SIS moves inwards! (it's a false move)

But by chance actually there is a curiosity: we could have expected a small movement more or less orthogonal to the PIG, but on the contrary, taking points a little far from the SMS and therefore not affected by the shear with PIG, we can see a small movement to the east! And indeed, by going to check the bathymetry of this area (SIS), we see that the bed sinks going east.  ;)

baking

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Re: PIG has calved
« Reply #1157 on: November 19, 2019, 11:25:30 PM »
So ... how many pixels thick (thin) yields how many arbitrary units of measurement (meters?)?
I get about 18-20 pixels at 20m per pixel, so 400 meters or just under.

baking

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Re: PIG has calved
« Reply #1158 on: November 20, 2019, 12:16:01 AM »
This is 17. vs. 18. Nov. way upstream.

The lower part is supposed to be grounded according to Sentinel. The upper part is floating.

Am i crazy or are they moving in opposite directions - as in the grounded part moves upstream?  ???

Sure looks like an artifact in the way the digital elevation model (DEM) was applied.  You can see that areas with opposite slopes are moving relative to one another.  This has to do with how the satellite images are taken at an angle and have to be corrected for elevation before they can be projected on a map coordinate.  See how the left slope of all the cravasses change in thickness at the same time.

Edit: Probably can't blame it on the processing.  More likely a difference in acquisition angles that the DEM was not able to fully correct for.  An image at the short range of the image will have a steeper angle then one taken at the far side of the range.  Since these features are too small for the DEM correction, slopes get foreshortened more at shallower angles.
« Last Edit: November 20, 2019, 12:29:44 AM by baking »

paolo

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Re: PIG has calved
« Reply #1159 on: November 20, 2019, 01:00:28 AM »
Thanks backing,
And my apologies for blumenkraft,

I had ignored the information in the post that the comparison was between the 18th and 17th and I had considered a more larger interval (with the most recent date on 18/11)

For this reason I did not understand his question.

Moreover, considering the date of the 17th instead of the 18th for the most recent image, curiosity, which I had reported, disappears. :)

But is very annoying that there are images with such artifacts!

Is this a mistake that should not be encountered and this image will be corrected later?

Otherwise its means that we can't use these images to evaluate the movements!

Or otherwise we have to check the consistency of the information with other images before using them for mesures!


baking

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Re: PIG has calved
« Reply #1160 on: November 20, 2019, 01:36:06 AM »
But is very annoying that there are images with such artifacts!

Is this a mistake that should not be encountered and this image will be corrected later?

Otherwise its means that we can't use these images to evaluate the movements!

I don't really use the Sentinel-2 images for numerous reasons.  Worrying about clouds, difficulty finding a rendering that works for ice, and just general annoyance with SentinelHub.  That said, I don't really know that much about Sentinel-2 and how to get images taken from the same angle.

What I do instead is use the Sentinel-1 radar images from PolarView.  No worry about clouds and I can pull individual images from particular satellite orbits.  This means that every image in a GIF I make is from the exact same angle.  (Unless I'm looking for movements less than 6 days apart in which case I bite the bullet and expect to deal with artifacts.)

Sentinel-1A makes the exact same orbit every 12 days.  Sentinal-1B does nearly the exact same orbit 6 days later.  That way you can get images every 6 days from the same angle.

You can probably do something similar with Sentinel-2, but I don't know how to do it and you also have clouds to deal with.  I'm sure Sentinel-2 has it's purposes, but I don't find it too useful for tracking the movement of ice.

paolo

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Re: PIG has calved
« Reply #1161 on: November 20, 2019, 04:09:58 AM »
Merci baking,

I just found, Sentinel2 makes the exact same orbit every 10 days  :)

blumenkraft

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Re: PIG has calved
« Reply #1162 on: November 20, 2019, 04:19:16 PM »
Sure looks like an artifact in the way the digital elevation model (DEM) was applied.

I think i know how those look like and i watched out for glues. I have to say i don't see them in those two shots.

Look at the shadows. They are pretty similar. Doesn't that suggest a similar angle and daytime?
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blumenkraft

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Re: PIG has calved
« Reply #1163 on: November 20, 2019, 04:23:37 PM »
And my apologies for blumenkraft,

No worries mate! :)

I had considered a more larger interval

Ya! The difference is amazing, isn't it? So much movement in only one lousy day...

Quote
But is very annoying that there are images with such artifacts!

I don't think those are artefacts (in this case).
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baking

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Re: PIG has calved
« Reply #1164 on: November 20, 2019, 05:33:29 PM »
I don't think those are artefacts (in this case).

Not sure how you can miss it.  The left-hand slopes all across the images appear brighter and wider in one image.  (Not sure which is the earlier one because they are not dated.)  This combined with the opposite effect on the rand-hand slopes makes all lower elevation points seem to shift between the pictures.

This is because one image was taken at a shallower angle and the DEM processing step was not able to account for elevation differences in the ice when the images were projected to orthographic coordinates.

Edit:  Take images from the exact same orbits and look at another spot.  You will see the same effect if it isn't perfectly flat.
« Last Edit: November 20, 2019, 05:42:34 PM by baking »

blumenkraft

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Re: PIG has calved
« Reply #1165 on: November 20, 2019, 06:22:46 PM »
because they are not dated

Sorry about that. Here is from Sentinel Playground with dates.

I included 2 more clear shots this time.
Click to play
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blumenkraft

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Re: PIG has calved
« Reply #1166 on: November 20, 2019, 07:01:26 PM »
Tidal wave caught in the act.

Click to play.
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blumenkraft

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Re: PIG has calved
« Reply #1167 on: November 20, 2019, 07:07:42 PM »
In the MOSAIC thread, the sperms are gone. (sorry for that)
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paolo

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Re: PIG has calved
« Reply #1168 on: November 20, 2019, 08:26:21 PM »
Blumenkraft,

As explained by baking (again thank you) you have to choose images corresponding to the same type of satellite passage, which for Sentinel 2 corresponds to 10 days

Attached:

A table for this area with usable days (coherent between them) for this area and, as an example of the area taken into account, the image of 03/11/2019

(click)
« Last Edit: November 20, 2019, 09:10:03 PM by paolo »

blumenkraft

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Re: PIG has calved
« Reply #1169 on: November 20, 2019, 08:31:57 PM »
Ok, i see. Thanks, Paolo.

Wait and hope for a cloud-free day it is. :)
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blumenkraft

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Re: PIG has calved
« Reply #1170 on: November 20, 2019, 09:03:35 PM »
This combined with the opposite effect on the rand-hand slopes makes all lower elevation points seem to shift between the pictures.

Sorry, Baking and Paolo, for nagging.

If i understand you guys correctly, points at the same elevation shouldn't shift, right?

In this GIF, we have the floating part on the left, and the grounded part on the right. I looked for cracks that presumably have sea level in between. I see what you say in the floating part. There the stuff between the cracks doesn't move. Not so with the other one though.

What do i overlook this time?
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baking

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Re: PIG has calved
« Reply #1171 on: November 20, 2019, 09:12:43 PM »
Wait and hope for a cloud-free day it is. :)

I think we can do better.  Here are Sentinel-1 radar images from November 7 and 19 from the same area.  Movement is top to bottom, East to West.  You can see the ice shelf downstream of the rift is moving, but not as fast as the glacier to the North (left.)

baking

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Re: PIG has calved
« Reply #1172 on: November 20, 2019, 09:26:30 PM »
In this GIF, we have the floating part on the left, and the grounded part on the right.

I can't find where your left "floating" image is from.

blumenkraft

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Re: PIG has calved
« Reply #1173 on: November 20, 2019, 09:58:29 PM »
Here you go, Baking. :)
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blumenkraft

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Re: PIG has calved
« Reply #1174 on: November 20, 2019, 10:01:30 PM »
I think we can do better.

You can do better! ;)

How do you align them for the GIFs?
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paolo

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Re: PIG has calved
« Reply #1175 on: November 20, 2019, 10:11:34 PM »
Blumenkraft

If you use images from Sentinel 2 you must choose images with intervals of a multiple of 10 days

baking

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Re: PIG has calved
« Reply #1176 on: November 20, 2019, 10:13:47 PM »
How do you align them for the GIFs?

I use the lines of latitude and longitude supplied by Polarview.  I register them as close as possible (less than a half pixel difference) in GIMP.

baking

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Re: PIG has calved
« Reply #1177 on: November 20, 2019, 10:38:24 PM »
If i understand you guys correctly, points at the same elevation shouldn't shift, right?

In this GIF, we have the floating part on the left, and the grounded part on the right. I looked for cracks that presumably have sea level in between. I see what you say in the floating part. There the stuff between the cracks doesn't move. Not so with the other one though.

What do i overlook this time?

So to be clear, the left hand image is a rift right at the shear margin of the glacier which is moving 12 meters per day.  The right hand image is the rift at the submerged rise, and which the Eastern (right) side of the rift should be assumed to be stationary.

Let's say that the ice at the bottom of the rifts is no more than a meter above sea level, so close enough for our purposes.

What I see as the problem is the ice at the bottom of the left-hand rift is absolutely stationary in your GIF, while it should be moving leftward by 12 meters.  The ice in the bottom of the right-hand rift should be practically stationary, but is instead moving rightward.

Seems like an alignment problem to me.

paolo

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Re: PIG has calved
« Reply #1178 on: November 20, 2019, 11:48:11 PM »
blumenkraft,

I take the opportunity to do my first test of animated gif, with the two consistent images of 29/10 and 18/11

(click twice)

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Re: PIG has calved
« Reply #1179 on: November 21, 2019, 05:54:06 AM »
I take the opportunity to do my first test of animated gif, with the two consistent images of 29/10 and 18/11

Thank You.  Your second image appears to be two pixels higher than the first image.  I tried fixing it by extracting the images from your GIF but in the process of making a new fixed GIF the colors become off.  My guess is that there is something funky happening with all the data compression.  If you could post clean images for both days, I will make another attempt.

Here is my somewhat artistic rendering.

baking

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Re: PIG has calved
« Reply #1180 on: November 21, 2019, 06:39:31 AM »
Here are Sentinel-1 radar images of the same area from about the same time period, October 26 to November 19 at 12-day intervals.  I've rotated it 90 degrees for easier comparison.

I don't see any significant differences that stand out.  Remember that Sentinel-2 is looking at surface features while Sentinel-1 is seeing through the snow cover to the ice below.  Thus, Sentinel-2 is able to see small features like snow drifts, but remember that snow drifts can move over time.  Movement of snow does not always mean movement of ice, even though it probably does 99% of the time.

paolo

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Re: PIG has calved
« Reply #1181 on: November 21, 2019, 11:15:42 AM »
Baking,

Attached the two images.
The two images: 1482x807, obtained from the Sentinel-Hub screen seem to me to be correct (you can check with the "500" block at the bottom right), is it a problem with the software to create the animated gif?

I used Active Gif Creator, which I downloaded last night after a very quick search for free software. Is it not good? Do I have to use something else?

Thanks in advance

Ps
I looked at my gif (with Firefox, maximum enlargement) and controlling the block "image day indicators" and I can't find any lag

« Last Edit: November 21, 2019, 11:36:11 AM by paolo »

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Re: PIG has calved
« Reply #1182 on: November 21, 2019, 11:44:32 AM »
What I notice is the difference in colors in both images, but this one is already in the images provided by Sentinel-Hub

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Re: PIG has calved
« Reply #1183 on: November 21, 2019, 12:06:38 PM »
On the other hand I notice a shift of images down in your gif (looking at the blocks "AGif UNREGISTERED", as well as the blocks "Dates of images")

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Re: PIG has calved
« Reply #1184 on: November 21, 2019, 03:34:13 PM »
Baking,

I checked the two images provided by taking two new copies of the same area and taking into account the movement of a control point between the two images provided and the movement of the same point between the two new images and the two movements are Identical.

I checked the URLs of the two new images and they are identical except for the date of course and therefore no changes of the coordinates, inadvertently, between the two (since it was a test I had not saved them, as I do usually, during the first image-taking).

For me both images, as well as the gif are good.



baking

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Re: PIG has calved
« Reply #1185 on: November 21, 2019, 04:04:32 PM »
For me both images, as well as the gif are good.

Paolo,

Thanks for posting the images.  As for the color, I think what happened is that somewhere along the way the images were compressed using a color palette in which the number of colors used in the images was reduced.  Then when I made the GIF the pallettes were combined for the two images resulting in poor color resolution.

The GIF below fixes that issue.  I use GIMP which is a free PhotoShop alternative available for PC, Mac, and Linux.  The only real issue with it is that it has many more features than I need.  Basically, I just use the "File/Open as Layers" menu to open multiple images as layers, The Move and Crop tools to align the images and resize them, and Filter/Animation/Playback to view the images before I File/Export them as GIFs.  One good thing is you can find many video tutorials on how to use GIMP for various tasks (as long as you know the name of what it is you want to do.)

The GIF below has the second image shifted down 2 pixels.  I just find it much easier to see what is going on.  I can't explain why it needed to be shifted, but I find this with satellite images all the time.  You need to line up the images at a fixed and hope that you chose a point that was really fixed and not moving.  I have some confidence from the Sentinel-1 images that the point I used was the most stationary point in the image.  I'm pretty confident that the Pine Island Glacier didn't just take a sudden jump to the North.

What I do know is that all or most of the motion I am seeing in the GIF below agrees substantially with the Sentinel-1 GIF taken over the same time period so I can be confident that what I am seeing is not an artifact of any one satellite acquisition or processing step.

blumenkraft

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Re: PIG has calved
« Reply #1186 on: November 21, 2019, 04:53:04 PM »
GIMP.

Oh, ok. Thank you. I guess i have to learn this ...
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Re: PIG has calved
« Reply #1187 on: November 21, 2019, 04:55:06 PM »
blumenkraft,

I take the opportunity to do my first test of animated gif, with the two consistent images of 29/10 and 18/11

This is awesome! Congrats on your first GIF! :)

As to consistent, i think i have understood the problem now. Thanks again for your patience. ;)
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blumenkraft

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Re: PIG has calved
« Reply #1188 on: November 21, 2019, 04:58:22 PM »
I wonder if there is no 'auto-align' software. We glacier watching people can't be the only ones with this need.

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paolo

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Re: PIG has calved
« Reply #1189 on: November 21, 2019, 05:19:43 PM »
Baking,

I do not align the images, the only thing I do is to modify, in Sentinel-Hub, the requested date so as not to introduce any manipulation!

What we see well in the corresponding URLs taken this afternoon for control (to be precise the two images I used today, and that correspond to the URLs below, are shifted vertically by two pixels related to yesterday's images, because I have only sought to visualize approximately the same area and that accuracy was not necessary considering the difference in the coordinates of the same point between the two images and the same lag does not change the difference in coordinates)

On the other hand, I do not know where you found points that do not move in the vicinity, the SIS moves and there are no rocks in the neighborhood.

Adresses URL :

https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=-75.31906814883804&lng=-99.94949340820312&zoom=12&preset=1-NATURAL-COLOR&layers=B01,B02,B03&maxcc=100&gain=0.2&gamma=1.0&time=2019-05-01%7C2019-11-18&atmFilter=&showDates=true

https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=-75.31906814883804&lng=-99.94949340820312&zoom=12&preset=1-NATURAL-COLOR&layers=B01,B02,B03&maxcc=100&gain=0.2&gamma=1.0&time=2019-04-01%7C2019-10-29&atmFilter=&showDates=true

« Last Edit: November 21, 2019, 06:05:34 PM by paolo »

baking

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Re: PIG has calved
« Reply #1190 on: November 21, 2019, 06:44:41 PM »
On the other hand, I do not know where you found points that do not move in the vicinity, the SIS moves and there are no rocks in the neighborhood.

You have a satellite and a the whole globe to work with, and you can't find a rock?  I'll tell you what, point it at your house and take two images 10 or 20 days apart and see if there was an earthquake that makes your house shake when you make a GIF.  Satellite images always need to be aligned.

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Re: PIG has calved
« Reply #1191 on: November 21, 2019, 07:03:40 PM »
I downloaded your full links and made two GIFS, one with no additional alignment and one after I aligned it as best I could.  Then I used a normal (10 fps) frame rate to accentuate the effect.  One makes you sick, the other one doesn't.

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Re: PIG has calved
« Reply #1192 on: November 21, 2019, 07:08:01 PM »
Baking, i'm convinced. Thanks a million.
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Re: PIG has calved
« Reply #1193 on: November 21, 2019, 07:53:23 PM »
Baking,

To check that Sentinel Hub works well and that the images are well aligned I searched for a mount and I did a test with Active GIF Creator and another with GIMP that you will find attached.

Results:
1.   Confirmation that Sentinel Hub works well, that there is no alignment to be made and just change the requested date. Clearly by being careful not to move the image afterwards and taking images with a lag of a multiple of 10 days
2.   The image of Active GIF Creator is more compressed, which can induce the effects you have reported (so I would switch to GIMP)

Conclusion:
1.   When we change the date in Sentinel Hub he will provide a new image using the coordinates of the old one, so it is he who will align the images and the result is good
2.   The alignment treatment of Sentinel Hub it may not be perfect (there is nothing perfect), but it is probably safer than a manual treatment on our part, treatment that should be reserved, in my opinion, only for cases for which we do not have (this is the case with Polar View images) or if it is bad.
In any case I can point out in a technical note accompanying the next images, if it seems useful to you: the method used, the URLs used and the possible treatments of the images

paolo

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Re: PIG has calved
« Reply #1194 on: November 21, 2019, 08:10:35 PM »
I just understood your point of view, it bothers you the fact that SSI is moving, but that's the reality, it moves towards the PIG and I don't see why eliminate this information that I prefer to keep

baking

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Re: PIG has calved
« Reply #1195 on: November 21, 2019, 08:17:36 PM »
it bothers you the fact that SSI is moving

Call me when it moves back.  ;)

paolo

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Re: PIG has calved
« Reply #1196 on: November 21, 2019, 08:27:37 PM »
Baking,

I forgot to say thank you for the "File/Open as Layers" information, which allowed me to create the GIMP gif
Before I could not and I did not want to waste time and for this reason I had looked for another software.

Again thank you and especially for the multiple of 10 days lag between images (I will calculate, as soon as I have time, the relative speeds of components SWT, SSI, PIG,.. and I would have made miscalculations without this information)



kassy

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Re: PIG has calved
« Reply #1197 on: November 22, 2019, 02:04:42 PM »
Interesting discussion, thanks!
Some light reading:

Pathways of ocean heat towards Pine Island and Thwaites grounding lines

...

In this study, we use an unprecedentedly high-resolution (200 m horizontal and 10 m vertical grid spacing) ocean model that resolves shelf-sea and sub-ice-shelf environments in qualitative agreement with existing observations during austral summer conditions. We demonstrate that the waters reaching the Pine Island and Thwaites grounding lines follow specific, topographically-constrained routes, all passing through a relatively small area located around 104°W and 74.3°S. The temporal and spatial variabilities of ice shelf melt rates are dominantly controlled by the sub-ice shelf ocean current. Our findings highlight the importance of accurate and high-resolution ocean bathymetry and subglacial topography for determining mCDW pathways and ice shelf melt rates.

...

https://www.nature.com/articles/s41598-019-53190-6
Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.

paolo

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Re: PIG has calved
« Reply #1198 on: November 22, 2019, 04:11:28 PM »
But it's a reminder to order  ::) ;)
Thanks for reporting the article to us

blumenkraft

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Re: PIG has calved
« Reply #1199 on: November 24, 2019, 12:11:36 PM »
Upstream crevasses 03. vs. 23. Nov. (yes, a multiple of 10 between the dates so it has the right angle ;) ).
Refugees welcome